Search in Rotated Sorted Array:在有转折的升序数列中搜索
2017-10-12 14:20
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Suppose an array sorted in ascending order is rotated at some pivot unknown to you beforehand.
(i.e.,
You are given a target value to search. If found in the array return its index, otherwise return -1.
You may assume no duplicate exists in the array.
思路:二分搜索,只不过因为有转折,所以判断那一部分是正常的顺序,那一部分有转折。如果target在正常部分,就正常搜索。
注意边界的判断,比如[1,3] target = 3,[1,2],target = 0,[1] target = 1这种。
class Solution {
public int search(int[] nums, int target) {
if(nums.length==0) return -1;
int s = 0;
int e = nums.length-1;
int m;
while(s<=e){
m = (s+e)/2;
System.out.println("nums[m]="+nums[m]+";m="+m);
if(nums[m]==target) {
return m;
}
//System.out.println("m="+m+";s="+s+";e="+e);
if(nums[s]<=nums[m]){//s到m之间正常有序,如果target在此区间内,正常二分,等号的目的是考虑[3,1]target=1的情况
if(nums[m]>target&&target>=nums[s]){
e = m-1;
}else{
s = m+1;
}
}else{//m到e之间正常有序,如果target在此区间内,正常二分
if(nums[e]>=target&&target>nums[m]){
s = m+1;
}else{
e = m-1;
}
}
}
return -1;
}
}注意,这几个边界条件我是硬试出来的
。。。晕了
(i.e.,
0 1 2 4 5 6 7might become
4 5 6 7 0 1 2).
You are given a target value to search. If found in the array return its index, otherwise return -1.
You may assume no duplicate exists in the array.
思路:二分搜索,只不过因为有转折,所以判断那一部分是正常的顺序,那一部分有转折。如果target在正常部分,就正常搜索。
注意边界的判断,比如[1,3] target = 3,[1,2],target = 0,[1] target = 1这种。
class Solution {
public int search(int[] nums, int target) {
if(nums.length==0) return -1;
int s = 0;
int e = nums.length-1;
int m;
while(s<=e){
m = (s+e)/2;
System.out.println("nums[m]="+nums[m]+";m="+m);
if(nums[m]==target) {
return m;
}
//System.out.println("m="+m+";s="+s+";e="+e);
if(nums[s]<=nums[m]){//s到m之间正常有序,如果target在此区间内,正常二分,等号的目的是考虑[3,1]target=1的情况
if(nums[m]>target&&target>=nums[s]){
e = m-1;
}else{
s = m+1;
}
}else{//m到e之间正常有序,如果target在此区间内,正常二分
if(nums[e]>=target&&target>nums[m]){
s = m+1;
}else{
e = m-1;
}
}
}
return -1;
}
}注意,这几个边界条件我是硬试出来的
。。。晕了
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